On 02-06-2017 10:05, Bruce Kellett wrote:
On 2/06/2017 5:31 pm, smitra wrote:
On 02-06-2017 04:54, Bruce Kellett wrote:
On 2/06/2017 12:00 pm, smitra wrote:
On 02-06-2017 02:07, Bruce Kellett wrote:
On 2/06/2017 7:28 am, smitra wrote:
On 01-06-2017 02:26, Bruce Kellett wrote:
On 1/06/2017 4:43 am, Bruno Marchal wrote:
Non-locality is not removed in MWI as you appear to believe.
For me the abandon of the collapse is the solution of the EPR
"paradox", and Aspect experience is somehow the confirmation of
our belonging to macrosuperposition.
The non-local (paradoxical) nature of EPR remains even without
collapse. As on the previous occasion we discussed this, you were
unable to demonstrate where the notion of 'collapse' is used in
Bell's
theorem - all Bell requires is that measurements give results,
and
that is what the whole of physics is based on: in MWI as well as
in
any other interpretation.
Bruce
In the MWI there are only trivial common cause like effects. There
is no non-locality in some mysterious sense like there is in the
CI where somehow there is a non-local effect but you don;t have
information transfer. The mistake most people make when arguing
that the MWI doesn't resolve the problem is that they can't get
their head around the fact that even when Alice and Bob meet and
Alice has not yet communicated everything that's necessary to Bob,
that the Alice that Bob sees has yet to collapse in the branch
corresponding to whatever she is going to say (Bob's consciousness
is thus located in many different branches of Alice, even if the
atoms in his body will be in different states due to decoherence).
I think that either you or someone else said something like this
when
this was last discussed. I have a couple of points to make:
1. This is not quantum mechanics, or the many worlds interpretation
of
QM. It is your own idiosyncratic theory that has no bearing on the
question of non-locality in QM.
2. Even in its own terms, this theory is nothing more than an
undisguised appeal to magic. You want consciousness to be unrelated
to
the decohered body. That conflicts with the overwhelming
experimental
evidence in favour of the supervenience on consciousness on the
physical brain -- they move in lockstep, so if your body has
decohered
having obtained a particular measurement result, all copies (if
there
be such) of this consciousness are conscious of the same
measurement
result. By the identity of indiscernibles, there is then only one
body
and one consciousness. That is what QM and MWI tell you, any
deviations are simple fantasy.
Bruce
Suppose Alice and Bob are robots with classical processors, the
states of each register can only be 0 and 1. Whatever Bob is
conscious of must then be contained in the bitstring that specifies
the state his processor is in. Decoherence has no effect on that
bitstring. Until that time that Bob asks Alice about her setting of
her polarizer, Bob's consciousness is exactly the same across the
different branches in which Alice gives a different answer,
False.
It's trivially true.
Bob's consciousness reflects the results he got. There are only four
branches: '++', '+-', '-+', and '--'. Bob's conscious state is
different for the two Alice '+' branches, and also different for the
two Alice '-' branches. So it is not invariant across Alice's
branches.
What matters for the MWI discussion is simply that after Bob has made
his measurement and he gets located in a branch corresponding to
whatever he has measured, that whatever Alice does is not going to
further localize Bob in a narrower set of branches due to decoherence
caused by Alice's measurements. Here you then do need to extract Bob's
consciousness from Bob's exact physical state. It's only when Alice
communicates the details that Bob's consciousness get's located in
Alice's branches.
despite rapid decoherence.
Real human beings can be expected to fit well within this model. It
is known that there typically is a lot of information present in the
unconscious mind that we're not aware of. So, your consciousness
could be identical across many branches even if your brain had split
and the unconscious mind is already diverging. Take e.g. experiments
where you are making a random choice and on the basis on functional
MRI scans the experimenters are able to predict your choice before
you have even made up your mind.
So, this is same good old QM in the MWI where an observer's
consciousness is modeled as a finite state machine described by a
finite bitstring. We can then work in the basis where the
observables for the bits of the bitstrings are all diagonal, this
then corresponds to the observer having a definite conscious
experience.
The definite conscious experience of relevance here is of observing
and recording the result of the spin measurement.
In practice, what this means is that you can be in a macroscopic
superposition long after decoherence has for all practical purposes
made the superposition inaccessible to be probed using interference
or other experiments.
For example, if a spin is polarized in the positive x-direction and
the z-component is measured, and I'm not aware of the outcome of the
result then my consciousness, as specified by the bitstring that
contains all the information that I'm aware of, cannot possibly
contain the result of the outcome of the measurement before I'm told
what the result is.
In a sector where my consciousness is described by bitstring X
after the spin has been measured, the state will have to be of the
form:
1/sqrt(2) |X> [|up, Universe(up)> + |down, Universe(down> ]
where Universe(up) and Universe(down) are different states of the
rest of the universe, but my consciousness is described by X and
this is not affected by the decoherence caused by measuring the
spin. In general there will be a summation of such terms where X
takes different values and Universe(up) and Universe(down) will then
depend on X, however, I can only ever find myself in a branch were X
takes some definite value, and any such branch will look like the
above state where the norms of both terms are equal.
That makes no sense, and is not the case in question. Alica and Bob
make measurements, observe the results and write them in their lab
books. Their subconscious mental states are of no relevance -- we
need
look only at their lab books. That is when the non-locality becomes
apparent.
Bruce
There is no problem here because as soon as the spin is measured by
Bob, he becomes entangled with the entangled spin pair; that in either
of his sectors the probabilities for Alice's results are immediately
affected is a rather trivial effect.
It might be trivial, but it is also non-local, which was my point. The
only way this can be avoided is for you to claim that Bell's theorem
is not valid. If that is your claim, then you are no longer talking
about quantum mechanics, and your theory is not valid.
Bruce
There is only an apparent non-locality in the MWI due to common cause
effects. The many words aspect leads to correlated branches and
everything stays strictly local. Bell's inequality is violated but that
doesn't imply that the MWI must have non-local features. The violation
of Bell's inequality only precludes local hidden variable models, but
the MWI is not a local hidden variable model.
If Bob measures his spin component of a two spin 1/2 particles in the
singlet state, then his measurement result is going to localize him in
the branch were Alice will make the opposite measurement if her
polarizer setting is the same. The fact that Alice measurement can be
said to be predetermined by what a space-like separated Bob has found is
not true in the MWI, because you have two Bob's in two branches. Alice's
results are then totally random even if Bob makes his measurement and he
can tell what Alice will find, because of the existence of the other
branch where he found a different result.
In a single universe theory, this implies non-locality, because of the
absence of local hidden variables. If local hidden variable were to
exist then you could say that Alice and Bob where to find whatever they
found anyway only due to their local interactions with the spins and
polarizers. But with that ruled out, whatever Alice will find is
information that just popped into existence when Bob made his
measurement.
This is then not similar to a common cause effect where Bob and Alice
are given a box containing either a white or black ball such that if Bob
gets a box containing the white ball, Alice gets the box containing the
black ball and vice versa. This can then be only be analogous to a local
hidden variable case.
In the MWI, the analogy with the black and white balls continues to hold
because we have two branches available where the boxes can be swapped.
Now, it does get more complicated when you consider different polarizer
settings, but then you need to specify exactly how these settings are
made. They can be predetermined, or they can be the result of other
quantum measurements, in which case further branchings need to be
considered.
Saibal
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